THE TRIGEMINAL NERVE

With all this discussion of receptors, you may be wondering where they are located in the mouth, throat, and nose, and what nerves they use for sending their messages.

The major nerve in question is the trigeminal nerve, also known as cranial nerve V. It gets its name from the fact that it has three major branches, which go to the upper, middle, and lower part of the face respectively. The area each branch serves is shown in this drawing  from Gray's Amatomy (1918). Green represents the ophthalmic branch, red(ish) represents the maxillary branch, which serves the inner part of the nose and the roof of the mouth, and yellow shows the area served by the mandibular branch, which serves the lower mouth and tongue.

Branches of the trigeminal nerve spread out all over the surface of the inside of the mouth, with small extensions into the taste buds.  The inside of the nose is also lined with branches of this nerve.

This nerve has two general functions: it sends sensations of touch, position, and pain, as well as warm and cold, to the brain from the face, eyes, and the inside of the nose and mouth; and it controls the muscles we use to chew.

In the inside of both mouth and nose, the sensations this nerve sends to the brain take on an added dimension (in addition to touch and the rest), because receptors on the nerve's endings that are activated by warmth and cold can also be activated by chemicals in the air and in our food. As a result, the trigeminal nerve modulates the sensations we experience from foods and beverages, now amplifying, now muting flavors, depending on which receptors are activated.

The trigeminal nerve enters the central nervous in the brainstem where it makes contact with the nerve centers responsible for making us awake, alert, and aware, for feeling emotions, and for focusing on tasks that require thinking.  Comfort foods are comfort foods — and black tea can be included among comfort foods —  in part because they activate the warm and hot receptors on our trigeminal nerve, which then links the flavor to warm fuzzy feelings. At the same time, you get a little wake-up call of increased awareness.

You may have found that sipping on a cup of green tea leaves you focused and refreshed.  By activating the cool/cold receptors, green tea sends a wake-up-and-pay-attention message via the trigeminal nerve, while we equate feelings of coolness with refreshment, in other words renewal of alertness.

Any questions?